git: kernel - Fix deadlock assertion panic with mmap/read combos
commit 283b944850fbb3421a77ef06aa121d066f5c8cad
Author: Matthew Dillon <dillon@apollo.backplane.com>
Date: Wed Jan 19 14:11:10 2011 -0800
kernel - Fix deadlock assertion panic with mmap/read combos
* Normally the uiomove() is called with the buffer locked. When
uiomove()ing into mmap'd memory this can cause a lock recursion and
panic, or a deadlock.
* Fix the problem by adding bqhold() and bqdrop() and adjusting the use
of the b_refs field to prevent the buffer from being invalidated,
allowing VFS VOP_READ operations to release the buffer prior to the
uiomove() into user memory.
* Adjust brelse() and getnewbuf() to do the right thing. Note that there
are two cases where b_refs can transition from 0->1. The VFS
release/uiomove case will only transition b_refs while the buffer is
locked while findblk() will transition b_refs at any time (while holding
the spin lock). We only care about retaining the VM pages in the
transition-during-locked case.
* Original problem reproducable with
grep -r --mmap SomeString /usr/pkgsrc
Reported-by: YONETANI Tomokazu <qhwt.dfly@les.ath.cx>
Summary of changes:
sys/kern/vfs_bio.c | 92 ++++++++++++++++++++++++++++-------------
sys/sys/buf.h | 7 ++-
sys/vfs/hammer/hammer_vnops.c | 16 ++++++-
3 files changed, 80 insertions(+), 35 deletions(-)
http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/283b944850fbb3421a77ef06aa121d066f5c8cad
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